Given the subtle nature of peroneal tendon subluxation or instability, these authors discuss the pathoanatomy of the condition, keys to diagnosis and emerging insights on surgical management.

Diagnosing peroneal tendon subluxation can be challenging as the majority of cases are subtle in their presentation and clinicians commonly misdiagnose the condition as a lateral ankle sprain. Prompt diagnosis and timely intervention are key to preventing chronic peroneal dislocation, instability and tears.

Of course, in order to recognize and treat peroneal tendon subluxation, one must have a firm grasp of the pathoanatomy and biomechanics associated with this condition. The lateral compartment of the lower leg is comprised of the peroneus longus and brevis muscles. They both travel posterior to the fibula within the fibular groove and at this level are in the same sheath with the peroneus brevis anteromedial to the peroneus longus. In the inframalleolar region, the peroneus longus and brevis muscles form separate sheaths around the peroneal tubercle, which can have various sizes and shapes.1 Inferiorly, the peroneal tendons are bound by the calcaneofibular ligament and the inferior peroneal retinaculum. The pathoanatomy of this condition lies within the integrity of the superior peroneal retinaculum, its contents and the ability to maintain those contents within the retromalleolar groove.

The superior peroneal retinaculum has a lateral, non-osseous roof and a floor comprised of an anterior osseous (retromalleolar groove) and medial non-osseous (posterior intermuscular septum of the leg) portions.2 As Standring described, the superior peroneal tunnel fibers extend superiorly, posteriorly and medially approximately 3.5 cm from the distal tip of the fibula and merge with the deep transverse fascia of the leg.3 Researchers have shown via cadaver dissection that the superior peroneal retinaculum, a static structure, has an impact on anterior ankle subluxation along with its dynamic, housed components: the peroneal tendons.4

The posterolateral portion of the distal fibula is bound by a retromalleolar ridge and superomedially by a retromalleolar tubercle. Multiple anatomic studies of the retromalleolar groove have detailed the shape to be most commonly concave. Edwards found an incidence of a concave groove in 82 percent of 178 specimens and 11 percent had flat surfaces.5 Athavale dissected 60 fibulas and 33 had concave surfaces, 21 were concave with a central ridge, two were flat and four were irregular.2

Interestingly, these authors discuss the pathoanatomy of this injury to be related not to the groove itself but to the fibular rotation.2,5 An externally rotated fibula would inherently relax the superior peroneal retinaculum and allow for peroneal subluxation. The internal rotation of the fibula would tend to tighten or stretch the superior peroneal retinaculum, impinging the peroneus brevis tendon against the retromalleolar tubercle, which would cause longitudinal tears. Adachi and coworkers also confirmed through magnetic resonance imaging (MRI) evaluation of 39 ankles that there was no significant difference in the morphological shape of the retromalleolar groove between patients with and without peroneal subluxation.6 Nonetheless, a normal fibular retromalleolar surface is made of smooth fibrocartilage and allows for tendons to glide freely.

Anatomic variants within the superior peroneal retinaculum may predispose a patient to recurrent or chronic instability and pain. The thinking is that a low-lying muscle belly causes instability through an “overcrowding” phenomenon although studies show it is the most common additional component within the tunnel and therefore is most likely a normal finding.7 Other anatomic variants include the muscle or tendon of the peroneus quartus, a ruptured peroneus brevis and even an accessory peroneal nerve.8-14 These all may contribute to peroneal pathology and instability in some form, and are often associated with subluxation.

What To Expect From The Patient Presentation And Diagnostic Imaging

Most clinical presentations of peroneal subluxation, dislocation or instability are subtle in nature and rely on an appropriate patient history and examination. Physicians can frequently misdiagnose these as lateral ankle sprains and a specialist must thoroughly evaluate these injuries.15 Monteggia first described this injury in ballet dancers in 1803.16 Two centuries later, athletes are still more inclined to sustain these injuries, especially in sports such as skiing, ice skating, soccer, basketball, gymnastics and rugby.17-21

The mechanism of these acute injuries is commonly a dorsiflexed foot and sudden or heavy contraction of the peroneal muscles. Acute symptoms of snapping or popping with pain and feelings of instability are common. Posterolateral ankle ecchymosis, edema and tenderness occur as well while forced eversion or activation of the peroneal tendons will incite pain.

If left untreated, these patients subsequently have chronic peroneal dislocation, instability and tears. Patients may be able to actively dislocate a peroneal tendon with or without pain. The pain is most commonly retromalleolar and associated with fullness or edema in this region from a peroneal split tear and tenosynovitis. Patients will also complain of instability and “giving way.”

A prudent diagnostician will also evaluate the patient’s lateral ankle ligament complex with an anterior drawer and talar tilt examination, comparing it to the contralateral limb. This complex also plays a role in the pathogenesis of peroneal instability. One should also evaluate appropriate hindfoot alignment and gait for fixed or functional varus.

Ankle and hindfoot radiographs are helpful in diagnosing varus malalignment, avulsion fractures, osteochondral lesions and osteophytes. Advanced imaging may assist in the diagnosis of osseous abnormalities associated with the retromalleolar groove and distal fibula. Szczukowski and colleagues utilized computed tomography (CT) in the diagnosis of suspected peroneal subluxation with good success.22

Magnetic resonance imaging is another non-dynamic imaging modality clinicians use heavily for foot and ankle pathology. When discussing MRI and peroneal tendons, one must be aware of the magic angle phenomenon. This common finding causes increased signal intensity within a normal tendon when the tendon fibers and magnetic vector form an angle of 55 degrees. Imaging the foot and ankle in slight plantarflexion (approximately 20 degrees) can decrease this effect.23 The MRI aids in the diagnosis of associated conditions such as lateral ankle ligament attenuation, peroneal tears and tenosynovitis, and hypertrophied peroneal tubercles.24

Specific peroneal tendon injuries and treatment are beyond the scope of this article but peroneus brevis tears (zone 1) occur in the retromalleolar groove and peroneus longus tendon tears (zone 2) occur within the cuboid tunnel.25 In their small series, Rosenberg and colleagues compared preoperative MRI evaluations to intraoperative findings.26 The authors identified eight true positives and one false positive, noting that the lateral fibular attachment is often thickened and difficult to differentiate from subcutaneous tissue. They concluded that superior peroneal retinacular injuries might be present in the face of normally positioned peroneal tendons.

These imaging modalities are great adjuncts but the proper diagnosis should occur clinically prior to imaging.

A Primer On Classifications Of Superior Peroneal Retinacular Injuries

Eckart and Davis described the most common classification for superior peroneal retinacular injuries in 1976.27 They reported on three types of injuries. Grade I injuries (51 percent) involved elevation of the retinaculum from the lateral malleolus, allowing the tendons to dislocate between bone and periosteum. Grade II injuries (33 percent) occurred when a fibrocartilaginous ridge was elevated with the retinaculum and the tendons subluxed between it and the fibula. Grade III injuries (16 percent) occurred with a small cortical fibular avulsion along with the retinaculum.

In 1987, Oden modified a grade II tear to be a retinacular tear as opposed to a periosteal elevation.28 The author added a grade IV injury pattern as a tear of the superior peroneal retinaculum from its posterior attachment.

What The Literature Says About Treatment

The management of peroneal tendon subluxation and instability is primarily based on a mechanical versus a functional mechanism. When the superior peroneal retinaculum is torn or elevated with or without a fragment of periosteum or bone, and the tendon(s) are unstable, the prevailing theory is to perform a direct repair of the superior peroneal retinaculum and secondarily assess the retromalleolar groove for concavity and deepen as necessary.

Acute injury treatment often includes a period of immobilization in a short-leg cast with the foot in a plantarflexed and inverted position to allow for the tendons to be in a relaxed position for six weeks. An aggressive physiotherapy program typically follows this period of immobilization.

Despite this, Escalas and coworkers reported that only 26 percent (10 of 38) of their acute cases improved after compression bandaging and immobilization.29 Eckert and Davis also determined through a treatment cohort comparison that it is not possible to determine the long-term stability of conservative treatment in acute injuries.27 Chronic injuries typically fail conservative treatment and there has been a success rate of less than 50 percent with non-surgical management.30 Therefore, the primary treatment for these injuries, acute or chronic, usually involves surgical intervention. Surgical repair of these conditions is optimal because of the typical patient demographic and the excellent results surgeons are able to achieve.

In acute injuries, direct repair of the superior peroneal retinaculum is the most common intervention. Eckert and Davis accomplished this with direct suturing of the anterior retinacular edge to the fibrous lip or through direct drill holes in the malleolar ridge if the lip had avulsion for grade I and II injury patterns.27 They reported a 5 percent redislocation rate. Summers and colleagues described a percutaneous technique in traumatic cases, in which surgeons placed Kirschner wires posterior to anterior in the fibula just anterior to the peroneal tendons and allowed indirect repair of the superior peroneal retinaculum.31 They noted no redislocation at follow-up in their series of nine patients. Marti also reported on five patients with primary repair, all of whom were pain-free at 3.5 years.32

One can correct chronic peroneal subluxation or peroneal instability through a variety of techniques described in the literature, typically involving tendon rerouting, fibula osteotomies or groove deepening.33-52

The aim of a tendon rerouting or tissue transfer technique is to reinforce the incompetent superior peroneal retinaculum and aid in retaining the peroneal tendons. These are often revision procedures with significant scar tissue and aberrant anatomy and the literature has described non-anatomic repairs with Achilles tendon slips, a calcaneofibular flap, a calcaneofibular ligament with a bone block, sub-calcaneofibular flap transposition, a peroneus brevis tendon slip and peroneus quartus.33-39

Bone block or fibula osteotomies may also prevent further subluxation and dislocation. In 1920, Kelly described an osseous procedure whereby one creates an osteotomy in the sagittal plane, splitting the distal fibula, and rotating the osteotomy clockwise and translating it posteriorly 6 mm.40 This creates a posterolateral fibular lip, which one would fixate with screws. Researchers have elucidated modifications to this procedure with good results.41,42 These are salvage procedures and require osseous union to occur, which will delay postoperative physiotherapy.

Groove deepening has become a well-integrated technique to indirectly reduce the propensity of the peroneal tendons to sublux in a more shallow retromalleolar groove. Researchers have also shown that these procedures decrease the overall pressure within the middle and distal retromalleolar groove.43 As Edwards found in his anatomic studies, the depth of the retromalleolar groove was approximately 3 mm and width was approximately 6 mm.5

In 1979, Zoellner and Clancy described the first groove deepening procedure, in which surgeons raised a cortical osteoperiosteal flap along the posterolateral distal fibula.44 With the tendon sheath opened and peroneals retracted anteriorly, surgeons curetted the cancellous bone to create a groove that was 6 to 9 mm deep. They tamped this osteoperiosteal flap back in position in a press-fit manner. This was the first direct deepening surgeons performed to reduce peroneal subluxation and all nine patients returned to their preoperative “athletic endeavors.” McGarvey and Clanton reproduced this procedure and reported a 30 percent complication rate.45 Porter and coworkers also reported on an osteoperiosteal flap and superior peroneal retinaculum augmentation in 14 patients with accelerated rehabilitation with no complications or recurrences.46

In 2009, Raikin reported on 14 patients with intrasheath subluxation diagnosed with dynamic ultrasound.47 He performed a posterior open trapdoor flap of the fibula at the level of the retromalleolar groove and used a rotary burr to deepen the groove. He repaired the flap with non-absorbable sutures through drill holes in the anterior fibula. American Orthopedic Foot and Ankle Society (AOFAS) ankle-hindfoot scores were improved over 33 months from 61 points to 93 points and nine of 14 patients reported excellent results.

Shawen and Anderson have also described and popularized indirect deepening procedures.25 The authors introduced the idea of a solid core drill bit and sequentially reaming the posterior cancellous fibula until one can use a tamp to deepen the groove 3 to 8 mm. This procedure is advantageous because it avoids an open osteotomy and surgeons can perform it with a low learning curve. It is imperative to confirm the drill is within the fibula and not in the lateral gutter, which one can avoid by first using a cannulated drill and guide wire.

Ogawa and colleagues performed a similar procedure on 15 patients and reported statistically significant poorer outcomes in patients requiring additional peroneal tendon repair versus isolated peroneal subluxation.48 Similarly, Saxena and Ewen reported on a cohort of 31 athletic patients who showed a tendency for a longer return to activity with additional peroneus brevis tear repairs.49 Again, multiple anatomic studies have shown a concave retromalleolar groove to be common and we have a low threshold for groove deepening.2,5

The literature is abundant with level III and IV studies on this topic. Given the complexity and paucity of peroneal subluxation cases, there has only been a grade I recommendation for the procedures described.50

A Closer Look At The Authors’ Surgical Technique

Our preferred technique for direct superior peroneal retinaculum repair with groove deepening involves a sharp excision of a 1 to 2 mm cuff of retinaculum at the posterolateral border of the fibula.51 Debride the peroneal tendons and repair them as necessary with absorbable sutures. Resect any atypical bulky, low-lying peroneus brevis muscle belly by electrocautery to prevent bleeding.

At this time, assess the retromalleolar groove for shape and bring the tendons through passive range of motion to evaluate for subluxation with circumduction and eversion of the ankle. With the tendons retracted, make a sharp periosteal incision at the tip of the fibula, lateral to the calcaneofibular ligament. Then insert a 3.5 mm solid drill in parallel to the retromalleolar groove and ream the distal fibula proximally about 2 to 3 cm. Then use a small curette to further debride and soften the fibrocartilage of the groove. Proceed to utilize a small, flat tamp to deepen the groove until attaining a desired depth (approximately 6 to 8 mm) to prevent dislocation.

Once the retinaculum is amenable to direct repair, resect the posterolateral border of fibula with a rongeur to allow for a fresh, bleeding bed. Then sharply elevate a lateral periosteal flap to assist in suture repair and perform a pants-over-vest suture repair technique, reinforcing the superior peroneal retinaculum with absorbable sutures. Take care to avoid inadvertently suturing the tendons when repairing the superior peroneal retinaculum.

What You Should Know About Post-Op Protocols

Postoperative protocols for peroneal subluxation and peroneal repairs are similar for us unless the operation is limited to a peroneal tenosynovectomy without repair. Initially, place the patient in a bulky Jones dressing with a plaster posterior splint in slight inversion with the ankle at 90 degrees. The patient is non-weightbearing for 10 to 14 days. At this point, one removes the sutures and the patient wears a non-weightbearing fiberglass short leg cast for four to six weeks. Following this period of immobilization, the patient will begin weightbearing in a high-top fracture boot, barring any corrective osteotomy.

The patient will then begin formal goal-oriented physiotherapy focused on passive range of motion and proprioception at eight weeks. There needs to be a strong and linked relationship with physiotherapy for optimum outcomes and satisfaction.
We recommend three two-week phases of physiotherapy. The first phase focuses on progressive weightbearing in a regular shoe and joint mobilization in an athletic ankle brace. The second phase focuses on proprioception and increasing range of motion. Subsequently, the focus shifts to strength and returning to preoperative activity. At the three-month mark, evaluate the patient for a formal return to activity assessment.

Pending satisfactory goal achievement, the patient then transitions into foot orthoses. If one did not perform a peroneal repair or subluxating peroneal repair, use a more aggressive postoperative weightbearing status. The patient transitions at the first postoperative visit into a tall fracture boot with physiotherapy beginning at three to four weeks postoperatively.

In Summary

Management of subluxing or dislocating peroneals in an acute or chronic situation, especially in an athlete, involves prompt diagnosis and intervention. The literature is abundant with level IV case series that support operative correction with a direct repair of the superior peroneal retinaculum and a groove deepening. More comparative, prospective studies need to occur for a higher level of recommendation.

Dr. McAlister is a Fellow of the Orthopedic Foot and Ankle Center in Westerville, Ohio.

Dr. Philbin is a fellowship-trained foot and ankle surgeon who is currently in private practice in Westerville, Ohio.